Solid State Phenomena Vol. 188

Abstract: In this work, the isochronal and isothermal activation energies for the primary crystallization process of Ti₄₀Zr₁₀Cu₃₄Pd₁₄Sn₂ bulk metallic glass have been studied by differential scanning calorimetry and determined using the Kissinger approach and the Johnson-Mehl-Avrami analysis, respectively. The activation energy for crystallization evaluated by the Kissinger method is 253 kJ/mol. Similar activation energy for crystallization was obtained from the viscosity measurements. The values of the differential Avrami exponent are also determined from the isothermal data. Assuming diffusion-controlled growth, it is shown that thermal treatment of the samples in the supercooled liquid region considerably influences the behavior of the nucleation rate during the crystallization process.

Abstract: This paper presents a mathematical model that describes the influence of the chemical composition on the glass forming ability of ferromagnetic alloys. Glass forming ability is given by the difference between the glass transition temperature and the primary crystallization temperature of the alloy. The glass forming ability is better as long this difference has a higher value. These temperatures were determined using differential thermal analysis.

Abstract: This paper presents some results for numerical simulation of the thermal field developed during rapid cooling of iron base alloy (Fe₇₃Cr₂Ga₄P₁₃Si₅C₃), to obtain bulk metallic glasses. Technology of rapid cooling gives the possibility to obtain bulk metallic alloys with an amorphous structure which can be used for industrial applications like magnetic shields. Validity of the numerical model of the cooling process was confirmed by the X-ray diffraction analysis. Once the model being validate, it can be used to optimize the rapid cooling process and casting mold geometry to be able to investigate the possibility to obtain larger amorphous bulk components.

Abstract: A research program has been completed in order to analyze structural changes during heating of amorphous alloys belonging to Fe-Ni-P system. Special attention has been given to thermodynamics and mechanism of crystallization, to determine some aspects of development for crystalline phases. Experimental material used to determine characteristics of crystallization consisted in long ribbons, 30 thick and 18 mm wide, fabricated by mean of “Planar Flow casting” as amorphous Fe₄₂Ni₃₈P₁₆B₄ alloy. Differential Thermal Analysis (DTA) and X-rays diffraction have been used to determine crystallization temperature of this alloy. Curves of differential thermal analysis for heating rates ranging between 1°C/minute and 20 °C/minute have been used to determine activation energy of crystallization.

Abstract: The polycrystalline nickel ferrite - NiFe₂O₄ has been obtained by ceramic route starting from a stoichiometric mixture of oxides (NiO and α-Fe₂O₃ powders). The obtained NiFe₂O₄ was subjected to high energy ball milling. The formation of NiFe₂O₄ by ceramic method and also the evolution of the powder during milling were studied by X-ray diffraction. The mean crystallite size of the NiFe₂O₄ continuously decreases with the increasing of the milling time and for all the milling time it is in nanometric range. The particles sizes are drastically reduced by milling process. For the milled samples, the particles size is ranging from tens of microns to few nanometers. The powder morphology and local chemical homogeneity were investigated by scanning electron microscopy (SEM) and respectively by energy dispersive x-ray spectrometry (EDX).

Abstract: The ZnFe₂O₄/α-Fe nanocomposite powders were obtained by ball milling starting from ZnFe₂O₄ powder synthesized by classical ceramic method and commercial iron powder. Two way of milling were used for the synthesis of the ZnFe₂O₄/α-Fe nanocomposite. In both cases after milling process the phases are relatively uniformly distributed in material and zinc ferrite mean crystallite size decreases from micrometric range up to 11 nm for the first milling mode and up 48 nm for second milling mode. The ZnFe₂O₄/α-Fe nanocomposite powders were compacted by Spark Plasma Sintering method (SPS). During sintering a reaction between nanocomposite phases occurs, thus leading to the formation of ZnO and FeO. The evolution of the powders during milling and stability of the nanocomposite phases was investigated by X-ray diffraction. The powders and compacts morphology and local chemical homogeneity were investigated by scanning electron microscopy (SEM) and respectively by energy dispersive x-ray spectrometry (EDX). The influence of the sintering parameters on the stability of nanocomposites phases is studied.

Abstract: High concentrations of metals in the natural environment associated with industrial activity and increased migration of metals may cause an increase in the concentration of metals in living organisms, especially in the bone tissue, which reflects their total concentration in the body. Physiological basis for this assessment is based on the fact that the skeleton serves as a major reservoir for ingested heavy metals integrating them into bone matrix during calcification and where they remain until the bone is remodeled or resorbed. Investigations on the bone can be focused on three structural levels: mezostructural, micro, and nanostructural. In this study, we used X-ray fluorescence (XRF) to measure the residual amount of heavy elements in bone particles, obtained by a widely used method. The bones used to perform the experiments were collected from local hospitals, following certain surgical coxofemural prosthesis operations (according to agreed procedures on patient privacy and medical ethics).Studies carried out on samples taken from humans have shown that the variability in bone chemical composition is depending on subject living area, which is essential for understanding the contribution of these factors on bone mass and constitution. Comparing values obtained with concentrations of metals in bones reported by other authors allowed us to conclude that EDPXRF method can be used to assess tissue concentrations of natural elements and the results provide a basis for evaluating metal loading of the human body.

Abstract: Nickel–titanium- group 5A metal (V, Nb, Ta, Zr) alloys are known as promising hydrogen-selective membrane materials. They can potentially be used in membrane reactors, which can produce high-purity H₂ and CO₂ streams from coal-derived syngas at elevated temperatures. The master alloys were prepared by arc melting using high purity metals in a Ti-gettered argon atmosphere. The alloys were melted several times in order to improve homogeneity. The ingots were induction-melted under a high-purity argon atmosphere in a quartz tube and graphite crucible injected through a nozzle onto a Cu wheel to produce rapidly solidified amorphous ribbons. Thermal stability of the Ni40Ti40Nb20 and Ni32Ti48Nb20 thin tapes has been examined using DTA analysis.

Abstract: A Ti-25Ta-25Nb β-type titanium alloy was subjected to thermo-mechanical processing and testing with the aim to observe the twinning deformation mechanism. Data concerning the evolution of twinning versus stress was obtained by SEM and micromechanical testing. Mechanical properties of the investigated alloy were also evaluated